Removal of heavy metals from CRUD and slime dam material using soil washing and bioremediation

[摘要] A substance called CRUD (Chalk River Unidentified Deposit) was deposited togetherwith gold tailings to the East Paydam tailings dam. Previous research conducted onthe material has shown that the crud leaches Mn and Ni at concentrations that areabove their acceptable risks limits as well as Zn which leaches at concentrationslightly below its acceptable limits thereby posing an environmental risk. The mainobjective of the research was to test the hypothesis stating that soil washing in serieswith bioremediation can be used to remove the heavy metals from the material fromthe East Paydam tailings dam.Various laboratory and pilot scale tests were conducted to investigate critical soilwashing and bioremediation parameters and their respective influence on thetreatment process. Laboratory work involved column tests and batch tests. These testswere crucial in determining the critical parameters for the pilot scale tests such as theselection of the suitable lixiviant from the four that were investigated. The optimalconcentration of the lixiviant was also determined together with the optimum soil:liquid ratio. These parameters were employed in the pilot scale tests. Pilot scale testsinvolved soil washing in series with bioremediation. The bacterial growth over thebioremediation period was also determined. Precipitation of the heavy metals fromleachate was investigated by varying the pH and temperature.Results showed that the soil from the East Paydam can effectively be treated by soilwashing in series with bioremediation. Oxalic acid was selected for soil washing ofthe payable slimes at a concentration of 0.001M. However, material that contains highamount of CRUD (deeper down the slime dam) required the relatively concentrated0.1M oxalic acid and mechanical agitation. Bioremediation was determined toincrease the amount of heavy metals that was leached from the material from the EastPaydam slimes dam. Precipitation of the heavy metals at a pH of 12 achieved up to98% removal of heavy metals from leachate.

[发布机构] Stellenbosch University